1. Field of the Invention
The present invention relates generally to distributed control digital communication and computer systems, to digital switching networks and to telephone exchanges for providing expandable subscriber line/trunk traffic capacity for toll, tandem, rural, local, concentration and expansion applications. The present invention also relates to multiprocessor or multicomputer communications systems in which certain of the data processing functions or other terminal processing functions are provided by one group of processors or computers while other processing functions associated with different and larger groups of the terminals are provided independently by a second pooled group of processors, while communication and data exchange between the two groups of processors or computers is provided over common transmission paths thru a digital switching network. The present invention also relates to multi-port switching elements characterized in that the ports thereof function either as inlets or outlets depending only upon the network application requirements for provided one-sided, two-sided or multisided switches in the network.
2. Description of the Prior Art
In modern telephone switching systems, it is presently required that data representative of the status of the subscriber lines and trunks served by such a switching system, together with required actions by the switch in response to various lines and trunks status conditions be stored. Representative data is path set-up through the network, subscriber class of service, trunk class of call, directory number to equipment number translations, equipment number to directory number translations, etc. In prior art centralized control systems, this data is available in a common memory, which is duplicated for security and reliability purposes and is accessible by common control computers for serial operations upon the extracted data. Multiprocessing common control systems of the prior art require more than one processor to access the common memory to obtain data at the same time, resulting in interference problems and an effective loss of throughput, which increases as the number of processors increases.
Decentralization of control and distributed data processing has evolved in light of the problems inherent in a centrally controlled system. A prior art switching system wherein stored program controllers are distributed throughout the system is described by U.S. Pat. No. 3,974,343. Another prior art progressively controlled distributed control switching system is described by U.S. Pat. No. 3,860,761.
Prior art systems have concentrated upon obtaining a high efficiency for the processing function, with multiprocessing providing increased processing capability; however, with resultant undesirable interaction between software packages wherein the modification or addition of features could interfere with the current working of other features in an unpredictable manner. A major reason for the problems of prior art common control architectures, whether or not multiple processors are used, is that stored program control processing functions are shared in time between a plurality of tasks which randomly occur on demand of the originating and terminating traffic, which does not provide for an efficient operation of the stored software packages.
In accordance with the present invention, there is no separately identifiable control or centralized computer complex, since the control for the switching network is distributed in the form of multiple processors throughout the subsystems, with such distributed processors providing groups of necessary processing functions for the subsystems serviced. Thus, groups of control functions for certain subsystems are performed by processors dedicated to those subsystems; however, other processing functions of the same subsystems which may be more efficiently performed by other processors are performed by such other processors.
Also, in accordance with the present invention, a switching network architecture is provided wherein not only are multichannel digitized PCM speech samples or data between one terminal and another carried by the network, but the same channels also contain the path selection and other control signals for the distributed control, which are carried on the same transmission paths thru the network. Every terminal, whether carrying data from a line or trunk or other data source is serviced by a terminal unit which contains all of the facilities and control logic to communicate with other terminals via other terminal units and to establish, maintain and terminate paths thru the switching network to other terminal units. All interprocessor communication is routed thru the switching network. A group switch containing switching elements providing both time and space switching is provided which is modularly expandable without disruption of service or rearrangement of existing interconnections to provide a growth from approximately 120 to 128,000 or more terminals, to accomodate increasing traffic load while performing as an effectively non-blocking network. A failed switch element is easily and automatically identified, isolated and bypassed by traffic.
In accordance with the present invention a group switch is provided in which multiport single sided switching elements are arrangeable in any inlet/output configuration for example, as 8.times.8 switches containing space and time switching in a ST configuration. The path selection throughout the network of switching elements is performed by control commands carried by the speech channels. Further, reflection switching facilities provided so that a path set up, for example, in a stage two switch, when no stage three is yet provided, will be reflected back via the speech path to form a folded network, while the outlets of the stage two switch remain available for future connection for network expansion. The expansion to a third stage would then require connection of the available outlets of stage two to the inlets of the future stage three switch.